Evaporator defrosting arrangement



Jan. 12, 1954 R. E. KING ETAL EVAPORATOR DEFROSTING ARRANGEMENT FiledDec. 12, 1951 Inventors Ralph E. K

Har-legy H.131 fe Their A-ttornqy.

Patented Jan. 12, 1954 EVAPORATOR DEFRGS'TIN'G ARRANGEMENT Ralph E. Kingand Ha ration of New York h rley H.- Bixler, Erie, Pa., 515- signers toGeneral Electric Company, a corpo- Application December 12, 1951, SerialNo. 2615174 16' Claims. (01. .62 126)' This invention relates torefrigerators or evaporators and more particularly to defrostingarrangements for evaporators.

In many household refrigerators, the evaporator for cooling the foodstorage compartment is exposed to the air within the compartment and isoperated at a temperature below the freezing point of water; As a resultthe moisture in the 'air within the storage compartment condenses on theevaporator and collects thereon in the form of frost. This layer offrost on thesurface of the evaporator has an insulating eifeot reducingthe efficiency of the evaporator in cooling the food storagecompartment. It is accordingly necessary to remove this frost from timeto time in order to prevent too serious a reduction in the operatingefficiency of the refrigerating apparatus. In many cases, thisdefrosting is accomplished manually by stopping operation of thecondensing unit and placing trays of warm water on the refrigeratedsurfaces of the evaporator. Defrosting in this manner is a somewhattime-consuming and disagreeable operation. By this invention arelatively uniform heating of the evaporator surface is accomplished anddefrosting is achieved without the necessity of using trays of warmwater and the like, and the time required for the completioii of theoperation is materially reduced.

Accordingly, it' is an object of this invention to provide an improvedarrangement for defrosting a refrigerator evaporator. I

It is another object of this invention to provide animpr'ovedarrangement for defrosting a refrigerator evaporator which maintains asubstafit'ially uniforrfi temperature throughout the entire evaporatorthe defrosting operation.

It is a further object or this invention to provide an improvedarrangement for defrosting a refrigerator evaporator including animproved arrangement' for insuring circulation of refrigerant in thesame direction through'theevapora tor under both heating and coolingconditions to prevent starving any portion of-theev'aporator ofrefrigerant. V

It is still anotherobject of this invention to provide an improvedarrangement for discharging defrost water from the'inte'rior of ane'vap' orator structure during each defrost period.

It is still a further object of this invention to provide an improvedarrangement for insuring a complete defrosting ofa-ll surfaces of theevaporator.

It is another abject-6f this invention- ;to' pro} vide an improvedarrangement for Supplying heat to anevaporator for defrosting theevaporator.

It is another object of this invention to provide an .improveddefrosting arrangement whereby a greater amount of defrosting capacityis supplied for surfaces on which the greater amount of frost collectsduring normal opera.- tion.

It is another object of this invention to provide an improved defrostingarrangement for minimizing the effect of the thermal mass of freezingtrays and their contents in retarding defrosting of the evaporator. v

Furtherob'jects and advantages of this invention will become apparent asthe following description proceeds and the featuresof novelty whichcharacterize this invention will be point-' ed out with particularity inthe claims annexed to andforming part of this specification.

In carrying out the objects of this invention, there is provided a wallstructure including bottom, rear, top and end walls defining a frozenfood storage compartment. Associated with this wall structure is aflooded evaporator having a header arranged near the top of the verticalwall and continuous serpentine tubing connected at both ends to theheader. One portion of the continuous serpentine tubing is secured tothe bottom wall of the evaporator and a second portion in seriestherewith is secured to the back wall, two end walls and top wall of theevaporator wall structure. The evaporator includes two closely spacedparallel sections spaced along the'seriescircuit thereof, and a singleheater is clamped in heat exchange engagement with both sections forvaporizing liquid refrigerant and cheating defrosting of the evaporator.Liquid refrigerant is supplied from the header to the first portionthrough a trap immediately pre ceding this first portion, and liquidrefrigerant from the condensing unit is injected into the evaporator at"the exit of the trap. The bottom wall of the" evaporator wall structureis provided with depressions between adjacent widely spaced parallelpasses of the serpentine tubing andhol'es we provided in the bottom ofthese troughs for draining defrostwater from the interior of theevaporator or frozen food compartment. The passe's'of tubing are moreclosely spaced along the bottom wall-of the evaporator, where thegreater amount of frost collects, than alongthe other walls of theevaporator.

For a better understanding of thisinvention, referent may he to theaccompanying flWhi'ch-Fig; 1- is a side elevation view i l ofa portionof a refrigerator incorporating an embodiment of this invention; Fig. 2is an isometric view of the evaporator, the walls upon which theevaporator tubing is mounted being shown in dotted lines for clarity;and Fig. 3 is a sectional view taken along the line 33 of Fig. 2.

Referring to the drawing, there is shown a refrigerator cabinet Iincluding an outer wall 2 and a spaced inner wall or liner 3, the innerwall 3 defining a food storage compartment 4. The access opening of thefood storage compartment is closed by a door 5.

In order to cool the food storage compartment 4, an evaporator 6 ismounted in the upper portion of this compartment. The evaporator 6includes a supporting wall structure including a bottom horizontal walli, a rear. vertical wall 8, a top wall 9 and two end walls It and H. Thewall structure defines a compartment 12 for the storing of frozen foodsand the like. A sloping baflle l3'is provided in spaced relationshipbelow the evaporator 6, so that air from the food storage compartmentrises upwardly at the forward portion thereof, fiows mainly between thebottom wall of the evaporator and the spaced bafile i3, and thendownwardly between the rear end of the baffle and the rear wall of thefood storage compartment 4.

The evaporator 6 is of the hooded recirculating type. The refrigeratingportion of the evaporator includes a header M which is positioned nearthe top of the rear vertical wall 8. The evaporator includes continuoustubing i5 arranged in generally serpentine fcrm and secured to thesupporting wall structure. One end of the continuous tubing i5 isconnected at 16 to the header M at a point below the normal level of theliquid refrigerant in the header. The other end ll of the continuoustubing (5 is connected in co 1.- munication with the interior of theheader is aboveYhe normal level of the liquid refrigerant therein. Bythis arrangement, liquid refrigerant flows from the header to the tubingl5 through the connection at it and vaporized refrigerant is dischargedinto the header at H.

The continuous serpentine tubing [5 includes a first portion l8 which isarranged in a generally horizontal plane and is secured to the lowersurface of the bottom wall I of the wall structure in any suitablemanner, as by brazing or welding. The tubing further includes a secondportion 19 which is arranged in series with the first portion Hi. Thissecond portion, in the form illustrated, extends in heat exchangeengagement with the rear wall 8, the end walls EU, I l, and the top wall9 of the wall structure. The tubing of this second portion I9 is securedto the exterior surface of these walls in any suitable manner, as bybrazing or welding.

Liquid refrigerant is supplied from the header to the first portion i 8of the continuous tubing [5 through a vertical section 20. The tubing isformed to provide a trap 21 at the bottom of the vertical section 26 andimmediately preceding the beginning of the first portion is of thetubing. The refrigerating system includes a condensing unit (not shown)and liquid refrigerant is supplied from the condensing unit to theevaporator through a capillary tube 22. The end 23 of the capillary tube22 extends into the tubing 1 5 at the exit of the trap 21, that is, atthe point where the exit end of the trap 2| joins the first pass of thegenerally horizontal tubing portion l8 adjacent the bottom wall I. Theend 23 is formed as an injector to inject liquid refrigerant into the 4evaporator circuit in the direction of the normal circulation of liquidrefrigerant in the evaporator.

The evaporator S and the tubing 15 thereof are exposed to the air withinthe food storage compartment 4 during operation of the refrigerator. Inorder to maintain a sufiiciently low temperature in the food storagecompartment 4 and in order to maintain a temperature within thecompartment i2 sufficiently low for the preservation of frozen foods,evaporators of this type are normally operated at a temperaturesubstantially below the freezing point of water. As a result, moisturein the air within the food storage compartment condenses on theevaporator and collects thereon asfrost, eventually forming a blanket ofsuch frost over the tubing and walls of the evaporator. This frost actsas an insulating medium, reducing the cooling effect of the evaporatorand reducing th efficiency of the refrigerating system. It is desirable,therefore, to remove this blanket of frost from time to time to maintainthe operation of the refrigerating system at a reasonabl highefficiency. In accordance with this invention, and arrangement isprovided whereby heat is supplied to the evaporator for vaporizingrefrigerant within the tubing and for assisting in circulatingrefrigerant through the tubing so that the vaporized refrigerant, as itreconclenses, gives up heat to the tubing for melting the frosttherefrom. Specifically, we provide a defrosting arrangement in whichheat is supplied by a single heater to the continuous tubing at twosections spaced along the length of the tubing. In the form of theinvention illustrated, one of these sections is located at the beginningof th first portion 18 of the evaporator tubing and the other section islocated at the end of this first portion l8, or stated otherwise, at thebeginning of the second portion l9 of the tubing.

Thus a single heater 24 is positioned in heat exchange engagement with afirst section 25 of the tubing i5 which is located at the beginning ofthe first, or horizontal, portion of the tubing, and with a secondsection 25 which is located at the end of the portion 18, or, in otherwords, at the beginning of the second portion I9 of the tubing. Thesections 25 and 26 are located in closely spaced parallel relationship.The heater 2 3 may be any type of device suitable for supplying heat tothe tubing and to the liquid refrigerant therein; for example, it may bethe sheathed insulating type of heating element sold under thetrade-marl: Calrod. Such heating elements include an electricalconducting element 21, a metal sheath 28 and an intermediate tightlypacked powdered insulating material 29,

The heater 23 is held in heat exchange relationship with the sections 25and 26 of the tubing i5 by a clamp 36. This clamp is somewhatchannel-shaped in cross section and may be secured to the bottom wall 7of the wall structure in any suitable manner, for example by screws 3|threaded into openings in the clamp 30. To provide a larger heattransfer surface contact between the heater Z l and the sections 25 and2B, the wall of these tubing sections adjacent the heater is deformed toprovide a concave portion or groove, as indicated at 32, conforming tothe circumference of the cylindrical heater 24. In the form of theinvention shown, one of the tubing sections, namely the section 26, issecured rigidly to the bottom wall l' of the wall structure in anysuitable manner, as by brazing or welding, as indicated at 33. The othertubing section 25 is f-re'e" of direct physical attachment: to thewall Ibut" is held in heatexchange relationship; with tnewallr" by th'e clamp30-, which not onl y presses the heater 24 into firm heat exchangecontact with the sections 25* and 26 butalso presses the section 25'into heat exchange contact with the wall-1.

During normal operation; refrigerantcirculates through the tubing I-S'ofthe evaporator in the direction indicated by the arrows, liquidrefrigerant-being supplied from the header through the vertical section20 and vaporized refrigerant returning to the header at the point I].Vaporized refrigerant is returned from the header to the condensing unitthrough a suction line 34'. Under such normal operation, the trap 2 I.assists in maintaining a proper direction of circulation or refrigerant,since it blocks flow of any vaporize'd refrigerant upwardly in thevertical section 20 The direction of circulation of refrigerant isfurther assisted, as mentioned above, by the injecting arrangement, at23, for liquid refriger'ant from the condensing unit.

When it is desired to defrost the evaporator, heat is simultaneouslysupplied by the single heater 24 to the tubing I5 at the sections 25 and25 which are spaced along the series circuit of the tubing. In the formillustrated, an electric heating element is employed, and such a heatingelement may be energized by supplying power thereto in any suitablemanner. It will be appreciated, however, that, within the scope of thisinvention, any other type of heating device for supplying heat to theevaporator in the arrangement described could be employed. Liquidrefrigerant vaporized by the heater at the section 25 circulates in thedirection indicated by the arrows through the first, or horizontal,portion I8 of the tubing, and the recondensation of the vaporizedrefrigerant as it passes through this portion of the tubing effectsmelting of the frost from this portion of the evaporator. Suchrecondensation is substantially complete by the time the refrigerant inits circuit reaches the section 26. Here heat is again supplied to thetubing from the heater 24, effecting a second vaporization of the liquidrefrigerant. This vaporized refrigerant circulates through the secondportion I9 of the tubing which is arranged in contact withthe end walls,the rear wall, and the top wall and, in recondensing, efi'ects meltingof frost from these areas of the evaporator structure. To assistdrainage of liquid refrigerant from the portion of tubing secured to thetop wall 9 of the evaporator wall struture, this top wall 9 is sloped tothe rear by a slight angle, for example in the order of three degrees.During defrosting, vaporized refrigerant condensing in the tubing of thetop wall 9 of the evaporator wall structure flows by gravity rearwardlyand downwardly into the header I4.

By this arrangement, a relatively uniform temperature is maintainedthroughout the length of the evaporator tubing during defrosting and acomplet defrosting of the entire evaporator surface is effected, thevaporized refrigerant circulating in heat exchange relationship with allfive walls of the compartment I2. The disposition of heater 24 in heatexchange relationship with two sections spaced along the series circuitof the continuous tubing I5 enables the use of a smaller size tubing anda smaller charge of refrigerant in the system. It will be noted that thetrap 2 I, which insures maintenance of the proper direction: ofcirculation of refrigerant normal 6 operation as described above, alsoeffects such maintenance of" theproper direction of circulation of"refrigerant during the: defrosting operation, since itwblocks flow upthe vertical section- 20 of refrigerantivaporized section 25 by theheater 24.

The significance of the flooded recirculating evaporator in thedefrosting operation should be noted. In cases where ak-series systemisemployed, that is where the capillary tube isconnected at oneend ofthe evaporator tubing and the header at the other, it is possiblefortheheaterto blow the tubing dry. Under these circumstances, continuedapplication of heat by the heater could burn out the heater orcause'damagetothe evaporator through local overheating. By ourarrangement employing a flooded recirculating evaporator where both endsof the evaporator tubing are connected to -the header, a supply ofliquid refrigerant to the tubing in the region of the heater is assured,and the possibility of the evaporator being blown dry with resultantdamage is minimized.

The tubing I5 is arranged on the wall structurewith portions of thetubing in heatexchange relationship with each wall and in a manner toinsure complete defrosting: of the wall structure. Thus the tubing I8includes sections 35- and 36 incontact with the endwalls III and IIrespectively of the evaporatorwall structure for effecting warming ofthese end walls and melting of any frost which may form thereon. Thesections 35 and 36 are arranged a particular manner on the end walls andthe passes of tubing of' the portion It on the bottomwall and of thesection 31 on the top wall are arranged in a particular relationshipwith respect to the end wall tubing to insure supply of heat to theentire evaporator end wall structure for defrosting. Thus it'will benotedthat the section 35' is positioned on the end wall III near thebottom thereof, this section 35 being connected to the tubing portion I8which in turn is arranged on the bottom wall 1 of the evaporator Wallstructure. During the defrosting operation, this section 35 supplies anample amount of heat to the lower portion of the end wall III. In orderto insure the supply of" sufficient heat to the upper portion of thisend wall II] for defrosting thereof, the section 31 of tubing on the topwall 9 includes a pass 38 which extends-adjacent and generally parallelto the edge of the top wall 9 at the junction of the top wall 9 and theend wall I0. By this relationship of the position in the section 35 andthe position of the pass 38, supply of heat of the entire surface of theend wall III is insured. Similarly, the section 36 is positioned at theupper portion of the end wall II, the sections 35- and 3B beingconnected by an upwardly inclined lengthtubing 39* which is secured inheat exchange relationship with the rear wall 8 of the evaporator wallstructure. During. defrosting vaporized refrigerant condensing in thesection-supplies heat'for insuring removal of defrost at least from theupper portion of the end: wall .8. In order to insure that the frost isalso completely removed from the lower portion of this end wall I I, onepass 40 of the tubing portion I8 on the bottom wall I extends adjacentand generally parallel to the edge of this bottom wall I which joinswith the end wall II'. The pass 40 insures supply of heat to the lowerportion of ,theend wall I II for effecting removal of. frost therefrom.-For .1 :further insuring complete ,namovatv or frost during thedefrosting operation, a front pass 4! of the portion H! of the tubing isarranged closely adjacent the front edge of the bottom wall 1. A flange42 of this bottom wall -1 is rolled over the pass 4! to insure good heatexchange relationship between the front edge of the bottom wall of theevaporator wall structure and the tubing. It has been found that wherethe front pass of tubing is arranged a substantial distance from thefront edge, frost does not completely melt from the area around thisfront edge during the defrosting operation. By the arrangementdisclosed, such complete melting of frost in this area is insured.Similarly, the tubing portion 19 includes a front pass 42a positionedclosely adjacent the front edge of the top wall 9 of the evaporator wallstructure. The flange 43 of the edge of this top wall structure 9 isrolled over the pass 421.! to insure good heat exchange contacttherewith. In this manner defrosting of the area at the front edge ofthe top wall 9 is also insured. It can be seen that by the arrangementdescribed, no section of the wall structure is thermally remote from thetubing and hence complete defrosting of the wall structure by thevaporized refrigerant circulating through the evaporator tubing isinsured.

An additional feature of the defrosting arrangement disclosed is thatthe spacing of the tubing passes on the various walls of the evaporatorstructure is varied so as to provide a closer spacing and hence morepasses of tubing in the area where the maximum frost collects. In arefrigerating arrangement of the type described, most of the air, asmentioned previously, rises upwardly at the front portion of the foodstorage compartment, circulates rearwardly between the bottom wall I ofthe evaporator and the spaced sloping bafile l3, and then passesdownwardly between the rear end of this baffle l3 and the rear wall ofthe food storage compartment 4. Accordingly, the maximum amount of frostcollects on the bottom wall of the evaporator, and much smaller amountson the remaining surfaces of the evaporator which do not receive thislarge amount of moist circulating air. In our defrosting arrangement,the parallel passes of the tubing which form the tubing portion l8 arepositioned much more closely than the passes of tubing which arearranged on the end walls, rear wall and top wall of the evaporator.Accordingly, a greater amount of heat is supplied to the bottom wall Iand to the remaining walls of the evaporator and, moreover, because ofthe. closer spacing of the passes of tubing adjacent this bottom wall,no portion of this bottom wall is as remote from the tubing as someportions of the other walls are from the tubing secured to these otherwalls. In this manner the maximum of defrosting capacity is supplied tothe area on which the maximum of frost collects.

During normal operation of the evaporator, frost forms on the innersurface of the wall structure as well as on the exterior surfacethereof. During the defrosting operation, this frost melts and collectson the bottom wali of the evaporator wall structure. In order to effectdischarge of this water from the interior of the compartment I2, thebottom wall 1 is shaped to provide a plurality of troughs 44. Thesetroughs are formed between successive relatively widely spaced parallelpasses 4|, 45, 46, 41, 48, and 25 of the first, or horizontal, portion18 of the tubins. Aplurality of spaced openings 49 are provided at thebottom of the troughs 44 for discharging water collecting therein to theexterior of the evaporator wall structure where it may fiow onto thesloping baiile i3 and be directed thereby toward the rear of the foodstorage compartment for collection in any suitable receptacle (notshown) or for discharge through a drain opening in the bottom of thecompartment 4 in a conventional manner.

The corrugated formation of the bottom wall I also contributes to theeffective removal of frost and further minimizes the melting of ice infreezing trays which are supported on this bottom wall. Thus, one ormore freezing trays, one of which is shown at 56, are supported on thebottom wall I and specifically on the top portions iii of the corrugatedstructure of this bottom wall. The successive passes of the tubingportion l8 are arranged in heat exchange relationship with the bottomwall I at these upwardly extending corrugations 5|, and hence the tubingis disposed closely adjacent the bottom of the freezing trays forfacilitating freezing of ice therein. Conversely, the portions of thebottom wall structure which are thermally more distant from the passesof the tubing portion l8, that is the portions providing the troughs 44,do not come in contact with the freezing trays. In this manner, thethermal mass of the freezing tray and its contents is ineffective forretarding flow of heat to the portions of the bottom wall 7, that is,the troughs 44, which are intermediate the successive passes of thetubing portion i8. Therefore, flow of heat to these portions of thebottom wall and defrosting thereof is facilitated by the particularcorrugated structure disclosed.

The heater 24 is deenergized by any conventional control device which isactuated by means of a temperature responsive bulb 52. This bulb 52 isconnected by a tube 53 to the control device for deenergizing the heater24 when a predetermined maximum temperature, Which insures completion ofdefrosting, has been reached. The bulb 52 is mounted on the end wall [0near the i bottom thereof by a clamp 54 which is riveted or otherwisesecured to the end wall [0. This bulb 52 is specifically located in aposition where presence of liquid refrigerant is assured and where heatfrom the heater 24 may reach this bulb by conduction through the wallstructure. Under some conditions, for example where the refrigerator islocated in an area where the ambient temperature may be as low as 40 F.,the running time may be so short that liquid refrigerant does not reachthe top of the evaporator. During defrosting the vaporized refrigerantmay condense in the case of the refrigerating unit in preference too thetubing of the evaporator. Accordingly, if the bulb 52 were under suchconditions positioned remote from the heater 24, and in a location wherepresence of liquid refrigerant were not assured, for example at the topof the evaporator, heat might not reach the bulb through the tubing insufficient quantity to insure deenergization of the heater 24.

The broad idea of a defrosting arrangement in which heat is supplied toa continuous evaporator tubing at two points spaced along the seriescircuit thereof is not our invention but is described and claimed in thecopending application of Charles S. Grimshaw, Serial No. 261,165, filedDecember 12, 1951, and assigned to the assignee of the presentinvention. The structural arrangement including the sloping bafiie isnot our invention butis, described and claimed in the coanswer 9pendin'gapplication o'f Harold P'JHarle, Serlal No. ?301,!756, 'fi1edJuly 80, i952 and "assigned to the General "Electric Company, theassignee :of the present application.

While a specific embodiment of this invention has been shown anddescribed, it is not intended that this invention be 'limited to theparticular construction shown and described and it is ihtended, by theappended-claims to cover-all r'n'odifications within the spirit andscope or this invention.

What we claim as new and desire to secure by Letters Patent of theUnitedStates is:

1. A flooded recirculating evaporator comprising a header and continuoustubing connected at'both ends to said header, said-tubing including Iafirst portion and a second portion-fin series'with said first portion,.one end of said tubing being connected to said header belowthe level ofliquid refrigerant therein for supplying liquid refrigerant to saidfirst portion, the other end of said tubing being connected to saidheader above the level of liquid refrigerant therein for conductingvaporized refrigerant from said second portion to said .header,and asingle heater disposed in heat exchange relationship with a section ofsaid first portionof said tubing near the beginning there- 'of, saidheaterbeing further disposed in heat exchange relationship with a secondsection of said tubing near the beginning of said second portion of saidtubing, whereby vaporization of liquid refrigerant and defrosting ofsaid evaporator is effected.

'2. In combination with a wall structure including bottom, rear, topandend walls-defining a food storage compartment, a flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends to said header, said tubing including a first portion secured tosaid bottom wall and a second portion in series with said first portionand-secured teat-least one of the remaining walls of saidwallstructure,one end 'of said tubing being connected to said header below the levelof liquid refrigerant therein for supplying liquid refrigerant to saidfirst portion, the other end of said tubing being connected tosaid'header above the level of liquid refrigerant therein for conductingvaporized refrigerant from said second portion to said header, and .asingle heater disposed in heat exchange relationship with a section ofsaid first portion of said tubing near the beginning thereof, saidheater being further disposed in heat exchange relationship'with asecond section of said tubing near the beginning of said second portionof said tubing, whereby vaporization ofliquid refrigerant and defrostingof said evaporator is effected,

3. A flooded recirculating evaporator comprising a header'and continuoustubing connectedat both ends to said header, said tubing including afirst portion and a second portion in series with said firstportion, oneend of said tubing being connected to said 'headerbelow the level ofliqu'id refrigerant therein for supplying liquid refrigerant to saidfirst portion, the other end of said tubing being connectedto saidheadera'bove the level of liquid refrigerant therein for conductingvaporized refrigerant from said second portion to said header, saidfirst portion of said tubing including two closely'spaced parallelsections substantially at the beginning and end respectively of saidfirst portion, and a single heater disposed in heat exchangerelationship with both of said sections for vaporizing liquidrefrigerant to defrost said evaporator.

'4.In1combination with a wall structure :in eluding bottom, rear, topand end walls defining a food storage compartment, a floodedrecirculating evaporator comprising aheader an'diicon tinuous tubingconnected at both ends to said header, said tubing including afirst'po'rtion secured to said bottom wall and a second portion inseries with said first portion and secured to at least one of theremaining walls ofsaid wall structure, one end of said tubing beingconnected to said header below the level of liquid refrigeran't thereinfor supplying liquid refrigerant to said first portion, 'the other endof said tubing being connected to said header above the level of liquidrefrigerant therein for conducting vaporized refrigerant from saidsecond portion 'to said header, said first portion of said tubingincluding two closely spaced parallel section's substantially at thebeginning and end respectively of said first portion, and a singleheater'disposed in heat exchange relationship with both of said sectionsfor vaporizing liquid rerrigerant to defrost-said evaporator. I 5.Incombination with a wall structureincluding bottom, rear, top and endwalls *definin'g a food storage compartment, 2, flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends-to said header, said tubing including a, first portion secured tosaid bottom wall-and a second portion in series with said first portionand secured to the rear, top and both end walls, one end of said tubingbeing connected to said header below the level of liquid refrigeranttherein for supplying liquid refrigerant to said first portion, theother end bf said tubing being connected to said header above the levelof liquid refrigerant therein for conducting vaporized refrigerant fromsaid second portion to said header, said first portionof said tubingincluding *two closely spaced parallelfsections substantially at thebeginning and entirespectively of said first portion, and *a singleheater disposed in heat exchangerelationship with both of said sectionsfor vaporizing liquid refrigerant to defrost said evaporator. g V

6. In combination-with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded recirculatingevaporator comprising a header and-conunuous tubing connected at bothends to said header, said tubing including a'first portion secured tosaid bottom wall and asecondpor'tionin series with said first portionand secured to at least one of the remaining walls of said ,wallstructure, one end of said tubing being connected to said header belowthe level of liquid refrigerant therein for supplying liquid refrigerant*to said first portion, the other end ofsaid "tubing being connected tosaid header above the level of liquid refrigerant therein for conducting"vapor ized refrigerant from said second portion-tosaid header, saidfirst portion of said tubing including two closely spaced parallelsections substantially at the beginning and end respectively of saidfirst portion, said tubing further including a per: tion forming a trapimmediately preceding said first portion, and a single heater disposedin heat exchange relationship with both of said sections for vaporizingliquid refrigerant to defrost said evaporator.

'7. In combination with a wall structure Zin eluding bottom, rear, topand end walls defining a food storage compartment, .a flooded relclirculating evaporator comprising a header and, continuoustubing'connected at both ends to said header, said tubing including afirst portion secured to said bottom wall and a second portion in serieswith said first portion and secured to at least one of the remainingwalls of said wall structure, said tubing including a vertical sectionconnected to said header below the level of liquid refrigerant in saidheader for supplying liquid refrigerant to said first portion, saidsecond portion being connected to said header above the level of liquidrefrigerant in said header for conducting vaporized refrigerant fromsaid second portion to said header, said tubing being formed to providea trap between said vertical section and said first portion, said firstportion of said tubing including two closely spaced parallel sectionssubstantially at the beginning and end respectively of said horizontalportion, and a single heater disposed in heat exchange relationship withboth of said sections for vaporizing liquid refrigerant to defrost saidevaporator.

8. In combination with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends to said header, said tubing including a first portion secured tosaid bottom wall and a second portion in series with said first portionand secured to at least one of the remaining walls of said wallstructure, said tubing including a vertical section connected to saidheader below the level of liquid refrigerant in said header forsupplying liquid refrigerant to said first portion, said second portionbeing connected to said header above the level of liquid refrigerant insaid header for conducting vaporized refrigerant from said secondportion to said header, said tubing being formed to provide a trapbetween said vertical section and said first portion, an injectorconnected to said tubing at the exit end of said trap at the point wheresaid trap joins said first portion of said tubing for injecting liquidrefrigerant into said evaporator in a direction facilitating circulationof refrigerant in said evaporator, said first portion of said tubingincluding two closely spaced parallel sections substantially at thebeginnning and end respectively of said first portion, and a singleheader disposed in heat exchange relationship with both of said sectionsfor vaporizing liquid refrigerant to defrost said evaporator.

, 9. In combination with a wall structure including bottom, rear, topand end walls defining a food storage compartment, a floodedrecirculating evaporator comprising a header and continuous tubingconnected at both ends to said header, said tubing including a firstportion secured to said bottom wall and a second portion in series withsaid first portion and secured to at least one of the remaining walls ofsaid wall structure, one end of said tubing being con nected to saidheader below the level of liquid refrigerant therein for supplyingliquid refrigerant to said first portion, the other end of said tubingbeing connected to said header above the level of liquid refrigeranttherein for conduting vaporized refrigerant from said second por tion tosaid header, said first portion of said tubing including two closelyspaced parallel sec tions substantially at the beginning and endrespectively of said first portion, and a single heater disposed in heatexchange relationship with both of said sections for vaporizing liquidrefrigerant to defrost said evaporator, said first portion furtherincluding a plurality of spaced 12 parallel passes, said bottom wallbeing depressed to provide a trough between successive ones of saidspaced parallel passes, said bottom wall having openings therein in thebottom of said troughs for draining defrost water from said compartment.

10. In combination with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends to said header, said tubing including a first portion secured tosaid bottom wall and a second portion in series with said first portionand secured to at least one of the remaining walls of said wallstructure, one end of said tubing being connected to said header belowthe level of liquid refrigerant therein for supplying liquid refrigerantto said first portion, and the other end of said tubing being connectedto said header above the level of liquid refrigerant therein forconducting vaporized refrigerant from said second portion to saidheader, and said first portion of said tubing including two closelyspaced parallel sections substantially at the beginning and endrespectively of said first portion, a single heater disposed in heatexchange relationship with both of said sections for vaporizing liquidrefrigerant to defrost said evaporator, and a clamp secured to saidbottom wall for pressing said heater into heat exchange relationshipwith both of said sections.

11. In combination with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends to said header, said tubing including a. first portion secured tosaid bottom wall and a second portion in series with said first portionand secured to at least one of the remaining walls of said wallstructure, one end of said tubing being connected to said header belowthe level of liquid refrigerant therein for supplying liquid refrigerantto said first portion, and the other end of said tubing being connectedto said header above the level of liquid refrigerant therein forconducting vaporized refrigerant from said second portion to saidheader, said first portion of said tubing in cluding two closely spacedparallel sections substantially at the beginning and end respectively ofsaid first portion, one of said sections being rigidly secured to saidbottom wall, the other of said sections being free of said bottom wall,a single heater disposed in heat exchange relationship with both of saidsections for vaporizing liquid refrigerant to defrost said evaporator,and a clamp secured to said bottom wall for pressing said heater intoheat exchange relationship with both of said sections and for pressingsaid other of said sections into heat exchange relationship with saidbottom wall.

12. In combination with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded recirculatingevaporator comprising a header and continu ous tubing connected at bothends to said header, said tubing including a first portion secured tosaid bottom wall and a second portion in series with said first portionand secured to the remaining walls of said wall structure, one end ofsaid tubing being connected to said header below the level of liquidrefrigerant therein for supplying liquid refrigerant to said firstportion, the other end of said tubing being connected to said headerabove the level of liquid refrigerant therein for conducting vaporizedrefrigerant from said second portion to said header, said first portionincluding two closely spaced parallel sections substantially at thebeginning and end respectively of said first portion, and a singleheater disposed in heat exchange relationship with both of said sectionsfor vaporizing liquid refrigerant to defrost said evaporator, said wallstructure including a first flange at the forward end of said bottomwall and a second flange at the forward end of said top wall, said firstand second portions including sections disposed adjacent said first andsecond flanges respectively, said flanges being rolled into heatexchange engagement with said last-named sections to facilitate transferof heat to the top and bottom forward edges of said wall structure formelting frost therefrom.

13. In combination with a wall structure including bottom, rear, top andend walls. defining a food storage compartment, a floodedrecirculatlevel of liquid refrigerant therein for supplying liquidrefrigerant to said first portion, said sec ond portion extending fromthe front toward the rear of said top wall and being connected at itsend to said header, and a single heater in heat exchange relationshipwith a section of said first portionof said tubing near the beginningthereof and in heat exchange relationship with a second section of saidtubing near the beginning of said second portion of said tubing forvaporizing ing evaporator comprising a header and continue ous tubingconnected at both ends to said header, said tubing including a firstportion secured to said bottom wall and a second portion secured to saidend walls and said top wall, said second portion including a sectionsecured to one of said end walls at the lower portion thereof and asecond section secured to the other of said end walls at the upperportion thereof, said second portion including tubing on said top wallextending adjacent and generally parallel to the junction of said topwall and said one of said end walls, said first portion including tubingon said bottom wall extending adjacent and generally parallel to thejunction of said bottom wall and said other of said end walls, saidfirst portion of said tubing including two closely spaced parallelsections substantially at the beginning and end respectively of saidfirst portion, and a single heater disposed in heat exchangerelationship with both of said lastnamed sections for vaporizing liquidrefrigerant to defrost said evaporator.

14. In combination with a wall structure including bottom, rear, top andend walls defining a food storage compartment, a flooded evaporatorcomprising a header and continuous tubing connected at both ends to saidheader, said tubing including a first portion secured to said bottomwall and a second portion in series with said first portion and securedto at least one of the remaining walls of said wall structure, and aheater disposed in heat exchange relationship with at least a section ofsaid tubing for vaporizing liquid refrigerant to defrost saidevaporator, said bottom wall being corrugated and being adapted tosupport a freezing tray on the upwardly extending corrugations thereof,said first portion including a plurality of spaced parallel passes oftubing, said passes being secured in heat exchange relationship withsaid bottom wall at said upwardly extending corrugations thereof wherebyrefrigeration is supplied through said passes for rapid freezing ofliquid in the tray, the downwardly extending corrugations being spacedfrom the freezing tray for minimizing the effect of the thermal mass of,the freezing tray and its contents in retarding melting of frost fromthe portions of said bottom wall intermediate said spaced parallelpasses of tubing.

liquid refrigerant to defrost said evaporator, said top wall beingsloped downwardly from front to rear whereby vaporized refrigerantcondensing in said second portion of said tubing drains V downwardly bygravity to said header.

16. In combination with a wall structure including bottom, rear, top andend walls defining ,a food storage compartment, a flooded recirculatingevaporator comprising a header and continuous tubing connected at bothends to said header, said tubing including a first portion comprising aplurality of passes secured to said bottom wall and a second portioncomprising a plurality of passes in series with said first portion andsecured to said rear, top and end walls, one end of said tubing beingconnected to said header below the level of liquid refrigerant thereinfor conducting liquid refrigerant to said first portion, the other endof said tubing being connected to said header above the level of liquidrefrigerant therein for conducting vaporized refrigerant from saidsecond portion to said header, said bottom wall being normally subjectto a greater amountof air circulation in heat exchange relationshiptherewith than said rear, top and end walls whereby a greater amount offrost forms on said bottom wall, and a single heater disposed in heatexchange relationship with a section of said tubing near the beginningof said first portion thereof and being further disposed in heatexchange relationship with a second section of said tubing near thebeginning of said second portion thereof for vaporizing liquidrefrigerant to defrost said evaporator, said passes of tubing on saidbottom wall being of greater number and spaced more closely than saidpasses of tubing on said rear wall, said end walls, and said top wallwhereby a greater amount of heat for defrosting is automaticallysupplied to the surface having the amount of frost thereon.

RALPH E. KING. HARLEY H. BIXLER.

References Cited in the file of this patent UNITED STATES PATENTS Numbergreater 1

